In a diamond, electron spins in a particular kind of colour centre, a nitrogen vacancy centre (NV centre), can be polarised and read out optically with the method of confocal fluorescence spectroscopy as demonstrated by A. Gruber et al. in “Scanning Confocal Optical Microscopy and Magnetic Resonance on Single Defect Centers”, Science 276, 2012, 1997. Moreover, as F. Jelezko et al. show in “Observation of Coherent Oscillations in a Single Electron Spin”, Phys. Rev. Lett. 92, 076401, 2004, such electron spins can be coherently manipulated with microwave fields.
M. D. Lukin et al. in “Nanoscale magnetic sensing with an individual electronic spin in diamond”, Nature 455, 644-647, 2008 report the use of NV centres in diamond as magnetometer to measure externally applied DC/AC magnetic fields. In “Nanoscale imaging magnetometry with diamond spins under ambient conditions”, Nature 455, 648-651, 2008, G. Balasubramanian et al. disclose a prototype nano-scale scanning probe with diamond spins, in which a nanocrystal containing a single NV centre is attached to the tip of a cantilever. G. Balasubramanian et al. report the imaging of the profile of the magnetic field produced by a nanometer-sized magnetic structure, with the spatial resolution about 20 nm. The method of optically detected magnetic resonance is used to measure the effect of a magnetic field on an NV centre electron spin.
In “A robust scanning diamond sensor for nanoscale imaging with single NV centres”, Nature Nanotechnology 7, 320-324, 2012, A. Yacoby et al. position a single NV centre at the end of a high-purity diamond nanopillar, which they used as the tip of an atomic force microscope. A. Yacoby et al. report scanning a single NV centre within tens of nanometers from a sample surface, and imaging magnetic domains with widths of 25 nm by determining the sample magnetic field along the NV axis.
In “Stray-field imaging of magnetic vortices with a single diamond spin”, Nature Commun. 4, 2279, 2013, V. Jacques et al. report the imaging of magnetic vortices in thin ferromagnetic films using NV magnetometry. V. Jacques et al. measure the three-dimensional distribution of stray magnetic fields above the magnetic nanostructures. The experiment is based on the same principle of NV-centre spin based magnetometry.
In “Nuclear magnetic resonance spectroscopy and imaging with single spin sensitivity” (submitted for publication), C. Müller et al. put a silicon layer on diamond surface, and use shallow implanted NV centers to detect 29Si nuclei. In their experiment they find very high magnetic field sensitivity at the level of single 29Si nuclear spins. C. Müller et al. create shallow NV centres (at the depth around 2 nm), and report their finding that these have good coherence properties for magnetic field sensing.
While the above works employed the principle of an NV centre magnetometer, none of the publications discloses the application of a colour-centre based diamond quantum sensor to detect the effect of pressure.
In “Electric-field sensing using single diamond spins”, Nature Physics 7, 459-463, 2011, F. Dolde et al. report using a single NV defect centre spin in diamond to measure a three-dimensional electric-field which is produced by a microstructure with an applied voltage, acting on a diamond point defect spin sensor. F. Dolde et al. measure the magnetic transition frequency change of a NV centre due to an applied a. c. electric field. The underlying mechanism is based on the direct coupling between NV centre spin and the electric field, which puts limit on the achievable sensitivity. The achieved sensitivity for the measurement of electric field is 202 (V cm−1) Hz−1/2.
In “Electronic properties and metrology of the diamond NV-centre under pressure”, Phys. Rev. Lett. 112, 047601, 2014, Marcus W. Doherty et al. report the direct effect of pressure on the diamond on spin properties of NV centres in diamond. Marcus W. Doherty et al. measure the dependence of the resonance frequency of an NV centre ground spin in diamond on the pressure at room temperature, and find that the zero field splitting of the ground state triplet of an NV centre is approximately a linear function of pressure with the linear constant dD(P)/dP=14.58(6) MHz/GPa, which results in the sensitivity for the measurement of pressure on the order of 1 MPa Hz−1/2. Marcus W. Doherty et al. also propose that the effect of pressure on the excited states of NV spin would be more prominent, and that the sensitivity for the measurement of pressure can reach the order of 0.1 kPa Hz−1/2. However, ultra-low temperatures (<12 Kelvin) are necessary in order to have sufficiently narrow optical lines and long excite state lifetime, in order to achieve the reported measurement sensitivity. This prohibits the biological and medical applications as well as most everyday applications e.g. in electronic skin.
In “Nanometer-scale thermometry in a living cell”, Nature 500, 54, 2013, M. D. Lukin et al. demonstrate nanoscale thermometry by measuring the change of the zero field splitting of the ground state triplet of an NV centre in nano diamond. M. D. Lukin et al. show the ability to measure the local thermal environment on length scales as short as 200 nm. Similar work is reported by David D. Awschalom et al. in “Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond”, Proc. Natl. Acad. Sci. U.S.A. 110, 8417-8421, 2013, and by J. Wrachtrup et al. in “High-Precision Nanoscale Temperature Sensing Using Single Defects in Diamond”, Nano Lett. 13, 2738-2742, 2013. The idea underlying these works is based on the fact that temperature changes the zero field splitting of the ground triplet states with a coefficient dD(T)/dT=74 kHz/K. The achieved sensitivity for the measurement of temperature is 5-10 mk Hz−1/2. A technique for the tracking, coherent manipulation, and readout out of an NV centre in cells was is disclosed in M. D. Lukin et al., Nature 500, 54, 2013, and in “Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells” by L. P. McGuinness et al., Nature Nanotechnology 6, 358-363, 2011.
The common piezo-sensors suffer from the electrical noise that limits their sensitivity, and their size is usually beyond the scale of micrometer or millimeter. The techniques of optical tweezers, magnetic tweezers and atomic force microscopy (AFM) suffer from the same disadvantage that the probe size is large (micrometer-millimeter). Moreover, AFM suffers from the drawback that it is limited to interfaces. The large size of the probe limits the spatial resolution that can be achieved and prevents the application of the techniques on a nanometer scale system. In addition, optical tweezers, magnetic tweezers and atomic force microscopy cannot be highly integrated. What is more, atomic force microscopy does not operate at ambient conditions and optical tweezers require a free space solution.